1. Field
The present disclosure relates to a semiconductor device and particularly to a power integrated circuit (power IC) provided with a driving circuit for driving a switching element on the high-side.
2. Description of Related Art
In mainly a low capacity inverter, for driving a switching element forming a bridge circuit for power conversion, a high breakdown voltage IC (HVIC) is used as a semiconductor device. The high breakdown voltage IC is generally provided with circuits such as a high-side driving circuit, a low-side driving circuit, a level shift circuit and a control circuit. The high breakdown voltage IC, in response to a signal inputted to the input terminal thereof, outputs a driving signal from the output terminal thereof which signal is inputted to the gate of the switching element and drives the switching element by turning-on and -off the element. In the bridge circuit for power conversion, the switching element in the high-side driving circuit is operated by receiving the signal from the high breakdown voltage IC, by which power conversion is carried out.
A high-side driving circuit is formed of a CMOS (complementary MOS) circuit with a p-channel MOSFET (insulated gate field effect transistor) and an n-channel MOSFET connected so as to be complementary to each other. The p-channel MOSFET is formed in an n-well region provided in a surface layer section of a p-type semiconductor substrate. The n-channel MOSFET is formed in a p-well region provided in a surface layer section of an n-well region.
The high-side driving circuit driving a high-side circuit is operated with a voltage VS taken as a reference voltage and with a voltage VB taken as a power supply voltage to output a driving signal from an output terminal on the basis of a signal received from the level shift circuit. The voltage VB is the highest voltage applied to the high breakdown voltage IC which voltage is kept to be on the order of 15V higher than the voltage VS by a bootstrap capacitor etc. in a normal state unaffected by noises.
The voltage VS is the voltage at the connection point (output node section) of a high voltage side switching element and a low voltage side switching element in a bridge circuit for power conversion. The voltage VS varies in the process of power conversion between zero volt and hundreds of volts and sometimes becomes a negative voltage.
In such a high breakdown voltage IC, various kinds of noises are inputted thereto which are produced by the operations of the switching elements. Thus, it is important to design a high breakdown voltage IC that withstands such noises to cause no malfunction and no inoperativeness. For enhancing noise withstanding capability, it is necessary to inhibit the operation of parasitic elements and, in particular, it is important to inhibit the operation of a parasitic element formed in the longitudinal direction of a substrate directly below a high-side region (around a high-voltage side switching element driving circuit). This is because a parasitic element formed in the longitudinal direction of a substrate has a large area that makes a large current easily flow therein.
In Patent Application Publication JP-A-2004-47937 (US 2003/0218186), a technology is disclosed which inhibits the operation of a parasitic pnp transistor by providing an n-type high impurity concentration buried layer between a p-type semiconductor substrate and an n-type semiconductor layer.
In Patent Application Publication WO2014/058028, a technology is disclosed which inhibits the operation of a parasitic pnp transistor due to a negative voltage surge by providing a p-channel MOSFET for clamping in an n-type well region.
It is an aspect of the invention to provide a new semiconductor device which inhibits the operation of a parasitic bipolar transistor in a high side driving circuit forming region.